1. Field of the Invention
This invention relates to an image processing method and apparatus and an image display method and apparatus and, more particularly, to an image display method and apparatus for restoring and reproducing an image from a received image signal.
2. Description of the Prior Art
Various television broadcast systems have become available and put into practical use in recent years. These include an NTSC system having an aspect ratio of 3:4 and 525 scanning lines, as well as television systems having a higher definition, such as an HDTV system having 9:16 and 1,125 scanning lines. In comparison with the NTSC system, the HDTV system involves about five times as much image information and has a wider screen. For these reasons, the HDTV system is advantageous in that an observer can enjoy a high-resolution, realistic picture.
However, there are limits upon the broadcast radiowave band and communication capacity. Consequently, when there is a large amount of information per frame, as in the case in the HDTV system, it is impossible to transmit this amount of information to a home directly. Accordingly, the information is transmitted upon being subjected to band compression using so-called distribution quality as a standard. This distribution quality is one in which the original picture quality obtained by TV photography at the studio is slightly reduced (i.e., in which the band is lowered).
FIG. 2 is a diagram showing one example of factors involved in such HDTV type studio picture quality and distribution quality. It will be appreciated from this diagram that the high quality of a picture of the kind provided by the HDTV system must be adopted as the distribution quality in order to fully enjoy it as a moving picture in the home. Since the HDTV system has a large number of scanning lines, is very fine and presents very little flicker, use thereof in the field of animation or the like is expected.
Generally, in case of a still picture, the viewer observes a single picture thoroughly for several seconds to several tens of seconds, and therefore picture quality equivalent to that at the studio is required. Besides an HDTV moving-picture display apparatus, an HDTV still-picture display apparatus has been provided and makes it possible to enjoy still pictures of studio quality.
This HDTV still-picture display apparatus has several frame memories. A received image is stored in whichever frame memory is designated from the transmitting side, and images are displayed by changing over from one frame memory to the next.
However, in this example of the prior art, the transmitting side transmits images upon absolutely designating addresses of the frame memories in the apparatus on the receiving side. Therefore, in a case where an image from one transmitting side is selected by channel changeover during reception of one program among programs sent from another transmitting side, or in a case where an image is replayed in mid-course as by a tape rewind operation when the image is being received while transmission data already stored on a video tape or the like is played back, there is the possibility that writing of data in a frame memory whose stored data is currently being displayed may be designated by the next item of image data, as a result of which new image information may be written in this frame memory. In cases such as these, the content of this frame memory will be rewritten while the image stored in this frame memory is being displayed. This means that the condition of the image in the course of being rewritten is displayed, thus resulting in an unattractive picture in which the image can be seen to temporarily dissolve or break down. Such problems are not limited to the aforementioned television broadcast systems, they happen to arise for other various system, e.g. video telephone and video conference and so on.